Various rotary electric machines as, for example, so-called brushless generators, may have a requirement that a rotor carry a resistor connected to some part of the electric circuit carried by such rotor. In brushless generators, a field winding is energized by direct current taken from a rectifier assembly which receives its input from an exciter as is well known. As various components in the rectifier circuit initiate or cease conducting, high voltage spikes are generated which may be of sufficient magnitude to cause damage to rectifier circuit components and also cause excessive electromagnetic interference.
To avoid this potential problem, it has been common to provide a shunt resistor connected in parallel with the field winding across the output of the rectifier through which the high voltage may be readily dissipated without appreciably affecting the total power level applied to the field winding. Since such generators are intended to be brushless, it is necessary that the resistor be carried by the rotor.
Heretofore, such resistors have typically been formed by winding resistance wire about a cylindrical spool which in turn is mounted concentrically with the rotor axis, usually on the rotor shaft. The difficulty with this approach is that the spool imposes definite limits on the axial length of the rotor which in turn result in the rotor having a length that may be longer than mechanically desirable and/or may impose mechanical limitations on generator components. In general, it is desirable that such generators be as compact as possible such that increases in the axial length of the rotor results in an increase in the axial length of the overall assemblage are not desirable. Frequently, too, particularly where such generators are to be employed in aircraft, system weight is a limiting factor such that increased mechanical strength or increased weight due to the use of larger bearings or the like which may be required by rotors of relatively long axial length is to be avoided.
The present invention is directed to overcoming one or more of the above problems.